A number of improvements have been introduced in universal mobile telecommunication systems (UMTS) wireless communications systems to increase the data rates available to end users. Following the introduction of high speed downlink packet access (HSDPA) for the downlink in Release 5 of the third generation partnership project (3GPP), high speed uplink packet access (HSUPA) was introduced as part of Release 6 of the 3GPP to improved uplink performance. The HSUPA uses hybrid automatic repeat request (HARQ) combined with short transmission time intervals (TTI) and fast scheduling to improve the uplink throughput and peak data rate over the new enhanced dedicated channel (E-DCH).
As wideband code division multiple access (WCDMA) is an interference-limited system, tight control of the uplink transmission power of every wireless transmit/receive unit (WTRU) is important. This is achieved via a combination of power control and grant mechanism. A grant for E-DCH transmission is a maximal power ratio that a WTRU may use to transmit on the E-DCH. The grant is translated directly to a transport block size. In this context, the grant can be interpreted as a right to create interference on the uplink. In HSUPA, the network signals a grant to each WTRU separately. There are two types of grants signaled by the network: an absolute grant and a relative grant. The absolute grant is transmitted over an E-DCH absolute grant channel (E-AGCH) by the serving E-DCH cell and carries an index to a grant table. The relative grant may be transmitted by any cell in the E-DCH active set over an E-DCH relative grant channel (E-RGCH). The WTRU maintains a serving grant that the WTRU uses to determine how much data may be transmitted during a given TTI. This serving grant is updated every time a new grant command is received either over the E-AGCH or the E-RGCH.
In addition to the grant mechanism, HSUPA also takes advantage of the macro-diversity by allowing non-serving E-DCH cells to transmit HARQ positive acknowledgement (ACK) to WTRUs over an E-DCH HARQ indicator channel (E-HICH) whenever the transmitted data is correctly decoded. The serving E-DCH cell (and the non-serving E-DCH cells in the same radio link set (RLS)) transmits an ACK or a negative acknowledgement (NACK) over the E-HICH for each received HARQ transmission.
The downlink control channel specific to HSUPA comprises the E-AGCH, the E-RGCH, and the E-HICH. For proper operation of the system, a power control loop using a fractional dedicated physical channel (F-DPCH) on the downlink and a dedicated physical control channel (DPCCH) on the uplink is established.
In order to meet the growing needs for providing continuous and faster access to a data network, a multi-carrier system that is capable of using multiple carriers for the transmission of data has been proposed. The use of multiple carriers is expanding in both cellular and non-cellular wireless systems. A multi-carrier system may increase the bandwidth available in a wireless communication system according to a multiple of how many carriers are made available. For instance, as part of the evolution of the technology, a new feature called dual-cell HSDPA (DC-HSDPA) has been introduced in the Release 8 specifications of the 3GPP. With DC-HSDPA, a Node-B communicates to WTRUs over two distinct downlink carriers simultaneously. It not only doubles the bandwidth and the peak data rate available to WTRUs, but also has a potential to increase the network efficiency by means of fast scheduling and fast channel feedback over two carriers.
DC-HSDPA significantly increases the throughput and efficiency of the downlink in the wireless communications systems. The introduction of DC-HSDPA further augments the asymmetry between the uplink and downlink in terms of throughput and peak data rates. However, no proposals have been made for the uplink. Therefore, it would be desirable to provide a method for exploiting the multiple uplink carriers for increasing the peak data rates and transmission efficiencies in uplink transmissions.